The compounds 2-(chloro, bromo, nitro or methyl)-4-methylsulfonyl-benzoic acid are intermediates that are useful in the preparation of a class of herbicidal compounds including 2-(2'-chloro-4'-methylsulfonyl)-benzoyl-1, 3-cyclohexanedione. These herbicidal compounds and their preparation from the acid chloride or acid cyanide of the above 2-(chloro, bromo, nitro or methyl)-4-methylsulfonyl benzoic acid and a substituted or unsubstituted 1,3-cyclohexanedione are described in several patents including U.S. Pat. No. 4,780,127.
U.S. Pat. No. 4,692,545 teaches a method of preparing compounds having the structural formula: ##STR2## wherein X' is chlorine, bromine, or nitro and R and R.sup.1 are alkyl by reacting a compound having the structural formula: ##STR3## wherein X' and R.sup.1 are as defined with an alkyl mercaptan (R--SH) including methyl mercaptan in the presence of an inorganic base and a polar aprotic solvent.
U.S. Pat. No. 4,704,467 teaches an indentical reaction except that it is run in the presence of an inorganic base and a phase transfer catalyst and a non-polar aprotic solvent. The alkyl esters of 2-(chloro, bromo or nitro)-4-methyl thiobenzoic acid are easily oxidized to the corresponding alkyl ester of 2-chloro-4-methylsulfonyl benzoic acid by conventional techniques.
The esters of 2-(chloro, bromo, or nitro)-4-methylthiobenzoic acid are converted to the corresponding benzoic acids by known techniques.